During the past 30 years, marine breeding has seen a formidable growth through establishment in countries naturally suited for fish farming, such as Norway, Chile, Canada, Ireland, and Japan. These countries have been able to offer easily accessible fish farming localities being well protected from the most wearing environmental forces in their long fjords, bays, or other regions of sheltered waters. Today, the aquaculture industry in these countries has grown to become a very successful industry.
In the last few years, several expert groups have concluded that the international growth potential for the industry is huge. This is the case not only for those breeds that are already being raised, but nonetheless for new breeds that will gradually grow to become successful commercial products. Moreover, it is also expected that the demand for fish and fish products will increase as a result of the rapid population growth. Internationally, among experts, it is commonly agreed upon that the main growth in the world's fish production must occur within sea farming, as the total take in the fisheries are approaching an upper defensible limit of about a 100 million tons per year.
An absolute requirement for further growth within the aquaculture industry is that the production capacity can be increased, and then for more breeds of farmed fish. With the current situation for the international fish farming industry, the potential for increasing the production capacity is very limited. This is due to the global lack of available sheltered inner coastal areas, and to that the existing technology is unable to provide for an efficient, safe, and profitable fish farming in open sea regions.
With the existing technology, coastal states without any form of, or with limited access to inner sheltered sea regions, are not able to develop large scale marine breeding. Existing fish farming installations commonly have a very simple configuration, generally including a seine freely suspended from a framework on the surface. Even at relatively slow current velocities however, the seines of these netpens undergoes appreciable deformations. At more exposed localities, the deformations may become severe. In addition, maintenance work and harvesting generally are both time consuming as well as expensive. Huge, heavy, and unmanageable seines also present a problem in connection with cleaning, impregnation, and replacement of the seine, as well as during harvesting. If the seine becomes damaged or worm, it is necessary to replace the entire seine or to bring it onshore for repair, which also involves removing the fish from the netpen. Furthermore, some maintenance operations require that parts of the work are performed under water, necessitating the use of expensive divers. This work is potentially dangerous.
The existing fish farming industry also has a problem in that diseases, infections, algal invasions, and various natural phenomena, such as “Super Chill”, air horns, and the like put stress on and kill the farmed fish, which every year brings along great losses for the breeders. The cause of these problems is a combination of insufficient technology, the fish farming localities, and natural phenomena. Open sea breeding as such can be beneficial to the fish. Increased current velocity will ensure a good water throughput rate in the netpen, result in a greater oxygen uptake and better trim for the fish, as well as an increased water replacement and thereby less fouling inside the netpen. In addition, the water temperature and salinity are generally more stable in the open sea outside the skerries. These are all factors that might improve the welfare, health and reproduction of the fish.
Outside the fish farming installations, the environment is contaminated by debris or waste, such as fodder residues and excrements from the farmed fish. Such waste (nutrients) accumulates in such big amounts that it is effectively pollution, and is thereby a problem both for marine animals as well as for human beings that travel in the sheltered water regions. In addition, many people also find the fish farming installations visually offensive.
Besides contributing to free up regions in sheltered waters and reduce the area conflicts, open sea fish farming also will provide beneficial environmental effects. Larger water depths, more rapid currents, and a greater distance to the shore will result in a reduction of the contamination of the sea floor and the inshore zone, as well as in a relief of the threat against wild extermination-threatened fish breeds, such as the wild salmon, for example.
As a consequence of the above problems, many people are convinced that the most important factor for a future sustainable growth within the aquaculture industry will be the ability to establish fish farms in the open sea outside the skerries. This would make possible the operation of a sound breed of a larger number of fish species in more countries, regardless of whether or not the particular country has access to a sheltered coastline.
Internationally, several attempts have been made at providing fish farming installations intended for deployment in open sea. Unfortunately however, none of these attempts have resulted in a commercially viable installation for operationally efficient, safe, and profitable fish farming outside the skerries. A few of the installations have had a limited commercial success however, although in more sheltered regions. The present situation confirms this in that the occurrence of open sea fish farms is in fact very limited, in spite of the fact that states having an exposed coastline have expressed high ambitions of running a large scale fish farming. Generally, the previous attempts at establishing open sea fish farming installations have failed because the installations have suffered from one or more essential shortcomings preventing a safe, ethical, and economically lucrative fish breeding. The most successful approach to an open sea fish farming installation is believed to be an installation provided by the American company Ocean Spar Technologies, disclosed in the U.S. Pat. No. 5,617,813. This installation has been used for fish farming in, among other countries, Hawaii, Ireland, and the United States of America. However, even though the installation has been utilized for raising a few broods of fish, it does by no means provide any substantial contribution to the large-scale establishment of aquaculture industry in the open seas outside the skerries. The shortcomings of the installation are, among other things, that it is difficult to maintain as much work must be performed under water by divers, that it is difficult to harvest the fish, that one has poor visual control of the fish from the surface, that it is impossible to dock to the installation with larger boats without damaging the installation, that the seine needs to be cleaned under water, that each day dead fish must be picked up by divers, and that the installation is limited in depth to about 35 meters, owing to the divers.
The U.S. Pat. No. 4,312,296 describes a spherical netpen. This installation never became a commercial success. The netpen is very small, having a volume of about 1200 m3. The construction is composed of aluminum stays and a grating or lattice. Aluminum as construction material is very rigid and brittle, and therefore susceptible to fatigue, which is unfavorable when the concept is to be implemented offshore, where the environmental loads are continual, cyclic, and large. In addition, this installation may only be lowered to slightly below the surface, and is thus exposed to considerable wave loading.
Moreover, the installation neither includes a working platform for personnel nor a docking station for boats.
The U.S. Pat. No. 4,312,296 relates to a spherical netpen having a vertically extending center pole.
The PCT application WO 92/03921, like the U.S. Pat. No. 4,312,296, relates to a spherical netpen having a through center pole. This netpen obviously bear close resemblances to the one in the above patent, both the construction material and the arrangement for buoyancy control through separate floatation bodies in each end of the center pole being identical.
The U.S. Pat. No. 5,617,813 relates to a netpen having a vertical center pole, as well as a weighting organ attached thereto.
Even today, examples are found of netpens that are being used for other purposes than fish farming, such as for storing various kinds of wild fish. The most common case is that inshore fishermen store the fish in netpens while awaiting delivery to an onshore reception facility. It can be easily appreciated that this use of netpens would be much more widespread if cost effective, efficient and enduring netpens became available for use in open sea. A future scenario could be that fishing boats deliver their catch, or parts thereof, on a regular basis to huge netpens by the fish fields outside central marketing places, thereby making it possible both to adapt to the current demand and to at any time deliver ultra fresh, or even living fish. A netpen having a permanently outstretched seine could also be used in transporting huge amounts of living fish. Currently, huge amounts of living fish are being transported in fish carrier boats or seine bags. However, a problem associated with such transport is that the fish are put under stress due to a large density of fish per m3. Transporting fish in a permanently outstretched netpen will not put the fish under the same stress, making it feasible to transport the fish over great distances, such as tuna fish from Europe to Japan, for example.